This invention relates to a digital signal recording apparatus for recording digital signals in a recording medium.
Currently, as an apparatus for processing digital signals adopted for civilian use, there are a digital audio tape recorder (DAT), a compact disc player (CD player), and a tuner for satellite broadcasting. In the digital signal processing apparatus, a variety of formats for signal processing in order are employed to convert analog signals into digital signals.
In general, when an analog signal is encoded and converted into a digital signal, processing such as sampling and quantization for converting an amplitude value of the signal into a discrete value is carried out. In implementing the sampling, a pulse generated at a constant cycle is used, wherein the cycle is called the sampling frequency. With the various sampling frequencies used in the sampling or the various numbers of quantization bits used in the quantization, different contents and volumes of data of the digital signal converted from the analog signal are produced.
For example, a digital audio tape recorder, that is, so-called R-DAT, for recording signals in slant recording tracks on a magnetic tape using a rotary head is provided with a signal processing format for converting an analog signal into a digital signal.
The signal processing format at the time of recording signals in the R-DAT has a total of five modes for audio PCM data: a mode called 48k mode wherein the number of channels is 2, the sampling frequency is 48 kHz, and the number of linear quantization bits is 16; a mode called 44k mode wherein the number of channels is 2, the sampling frequency is 44.1 kHz, and the number of linear quantization bits is 16; a mode called 32k mode wherein the number of channels is 2, the sampling frequency is 32 kHz, and the number of linear quantization bits is 16; a mode called 32k-4CH mode wherein the number of channels is 4, the sampling frequency is 32 kHz, and the number of non-linear quantization bits is 12; and a mode called 32k-LP mode wherein the number of channels is 2, the sampling frequency is 32 kHz, and the number of non-linear quantization bits is 12.
The variety of formats at the time of recording digital signals as described above may be classified into two groups, that is, a standard mode (SP mode) and a long-play mode (LP mode). In the group of SP mode, plural kinds of sampling frequencies are used, and quantization is carried out with the number of quantization bits being 16 or 12. On the other hand, in the group of LP mode, the sampling frequency of 32 kHz is used, and the number of quantization bits is set to 12. Among the above-mentioned variety of formats, only the 32k-LP mode is of the LP mode, and all the other modes belong to the group of SP mode. Since the data volume of the LP mode is about half the data volume of the SP mode, the recordable time of the recording medium of the LP mode is approximately twice as long as that of the SP mode.
There is an interface format for inputting and outputting digital signals of a digital audio signal recording and reproduction apparatus for civilian use. This digital interface is format constituted as shown in FIG. 1, in consideration of the connection to all devices for inputting and outputting the digital signals as well as the connection between DATs. In this format, an L channel (stereo left channel) and an R channel (stereo right channel), both called sub-frames, are combined to constitute one frame. The signals of the L channel and R channel are time-division multiplexed in a manner of L, R, L, R, . . . , and 192 frames constituting one block are transmitted.
Meanwhile, a preamble indicated by B in FIG. 1 is set when it is both the beginning of the block and the beginning of Channel L. A preamble indicated by M is set when it is not the beginning of the block but is the beginning of Channel L. A preamble indicated by W is set when it is the beginning of any channel other than Channel L.
One sub-frame is constituted by 32 bits, as shown in FIG. 2, normally 20 bits of which and a maximum of 24 bits of which are starting from the LSB, as audio data. The remaining 4 bits are allocated into bits V, U, C, P as synchronization signals. The C bit among the synchronization signals is called a channel status bit, which defines a property of the data. Meanwhile, 4 bits following the synchronization preamble of 4 bits are auxiliary bits.
The channel status bit, which is the C bit, is transmitted for each channel with 192 frames as a unit, as shown in FIG. 3. The channel status bit includes important information, such as, a category code for expressing copy inhibition and types of transmission equipment, channel number, and sampling frequency.
The above-mentioned format of a digital audio interface is described in detail in a Japanese periodical, "NIKKEI ELECTRONICS," Jun. 1, 1987, pp. 109-118.